Color filters can be used for liquid crystal displays (LCD), optical filters for cameras, and the like. Color filters can be fabricated by coating a fine region colored with three or more colors on a charge coupled device or a transparent substrate. The colored thin film can be fabricated by dyeing, printing, electrophoretic deposition (EPD), pigment dispersion, and the like.
The color filter is prepared through many chemical treatments during the manufacturing process. Accordingly, in order to maintain a pattern formed under the aforementioned conditions, a color photosensitive resin is required to have a development margin but chemical resistance and thus, to improve yield of a color filter.
A conventional color liquid crystal display (LCD) is generally fabricated by preparing a color filter substrate for displaying a color image separately from an operating substrate on which a thin film transistor (TFT) is disposed and then, binding the color filter substrate and the operating substrate together. However, since there can be low arrangement accuracy during the binding step, conventional color liquid crystal displays can require a shading layer with a large width. Accordingly, it is difficult to increase the aperture ratio (a ratio of an active light-emitting area to a total pixel area). In addition, because the glass substrates of LCDs and LCD screens have recently become larger, it takes longer for a liquid crystal composition to cover the front side of the substrates during vacuum injection of a liquid crystal.
A method has been suggested to sharply decrease the time needed to print a seal material and drip a liquid crystal to form an over-coat. The method, however, can result in sharply deteriorated arrangement accuracy.
A method of forming a color filter on the operating TFT array substrate of a TFT color liquid crystal display (LCD) has also been suggested. Since this method does not need a color filter substrate and fabricates a transparent substrate through sputtering and binding two substrates, it has an advantage of simplifying the arrangement and increasing an aspect rate.
However, when a color filter is formed on a TFT array substrate, a pixel electrode is formed on the color filter in a photolithography method by using a common positive photoresist. Accordingly, the resist layer needs to be removed after forming the electrode. In other words, a pixel electrode is formed by forming a transparent electrode layer on color pixels of a color filter, coating a positive resist composition thereon, and patterning it, exposing it to light, and developing it. Then, the resist layer remaining on the pixel electrode should be peeled and removed with a resist stripper. Accordingly, the positive resist composition requires resistance against the resist stripper. Then, the resist layer remaining on the pixel electrode should be peeled and removed with a resist stripper. Accordingly, the positive resist composition requires resistance against the resist stripper.
Conventionally, a pixel electrode is fabricated by forming a transparent layer (a pixel protective layer) having stripper-resistance on a color filter. In addition, a pixel electrode can be fabricated without coating a pixel protective layer by treating a stripper at a low temperature for a longer time to decrease the stripper's influence on a color filter.
However, these conventional methods have problems of deteriorating yield rate and production efficiency, since they require more processes and longer time. In order to solve these problems, another method has been suggested, which includes using a radiation-sensitive composition with an expansion rate of less than 5% against a stripper to remove a cured layer forming a color layer in a COA (color filter on array) method. Further, a color filter can have improved thermal polymerization cross-linking effects by using a multi-functional alicyclic epoxy compound as a thermal polymerization cross-linking agent and a benzophenone-based peroxide as a thermal polymerization initiator. According to this method, a color filter can be cured at a low temperature for a short time and thereby, can have excellent durability and close contacting (adhesion) properties. However, as the demand increases for larger screens with higher image quality than can be produced using conventional methods, there is also an increased need for a color filter with a higher aperture ratio and higher performance.